Single-use systems are being increasingly used in the medical or laboratory technology as compact medical functional devices such as cassette systems or blood treatment cassettes in which liquids and gases, in particular medical fluids and blood, flow in channels and chambers. If they are provided for a single use, one speaks of disposable cassettes or one-way cassettes.
The blood treatment cassette is sterilized prior to use, for example by means of a sterilization fluid (steam, liquid, gas, etc.), which flows through the blood treatment cassette.
During steam sterilization of the blood treatment cassette, for example in a sterilization container of an autoclave, the air in the container is completely replaced by superheated steam in several cycles. The sterilization container having the blood treatment cassette (to be sterilized) therein is evacuated by vacuum pumps and then flushed with steam at elevated pressure. The superheated steam condenses on the surfaces of the blood treatment cassette which are to be sterilized. Depending on the size and design of the blood treatment cassette, this process is repeated according to need. It is important for the sterilizing effect that steam condenses on all surfaces of the blood treatment cassette. If the blood treatment cassette comprises voids or cavities having flexible elements, this can lead to undesirable deformations during the various phases of sterilization due to the large pressure changes. In particular, a blood treatment cassette having large cavities of a hard part of the blood treatment cassette (such as chambers or channels) which are covered by means of a film, is in this respect a particular challenge. The flow paths to the cavities comprise partly narrow areas (such as hydrophobic membranes or long, thin tubes) which have the effect that during pressure changes in the interior of the cavity there is a different prevailing pressure than that in the exterior. The additionally prevailing high temperature during sterilization may thus lead to irreversible deformation of the film.